This project will examine the effect of malignancy (breast-cancer, colon cancer and lymphoma) on several mechanisms of human monocyte cytotoxicity. Monocytes will be isolated from the peripheral blood in normal donors and patients and examine the following assays: 1) Monocyte antibody-dependent cytotoxicity to red cell targets; 2) Monocyte antibody-dependent cytotoxicity to malignant tumor cell line: 3) Monocyte inhibition of thymidine uptake by tumor cell; 4) Monocyte direct cytotoxicity to tumor cell target; and 5) Monocyte cytotoxicity to tumor targets as reflected by number of viable tumor cells. These studies will be done in breast carcinoma and colon carcinoma patients prior to and after surgical resection disease as well as in patients with extensive disease (metastatic breast cancer and malignant lymphoma). Finally, the effect of successful chemotherapy in patients with breast carcinoma and malignant lymphoma will be examined following objective response.